Dovetail joints have been utilized for many hundreds of years to lock the ends of two boards, usually when the boards are at 90 degree angles with respect to one another. Such dovetail joints are extremely strong because they are formed with interengaging projections and slots that taper in both orthogonal directions. Dovetail joints can either be full joints, or they can be blind joints where the tongues on one board engage in blind or closed end slots in the other board.
While such dovetail joints have a high strength, they are not really suitable for visible external joints because of their unattractive and rather commonplace appearance. Therefore, to a large degree dovetail joints are utilized in furniture areas, for example, mostly at joints that are not externally visible.
Another disadvantage in dovetail joints is that they cannot be utilized with miter joints because of their fundamental construction, and of course, miter joints are usually utilized at corner locations that are exterior to the piece, and thus visible, where appearance is important.
Another disadvantage in dovetailing systems is that the machinery utilized for guiding the routing tool that forms these double-tapered slots in the board ends is extremely expensive. These tool guiding systems include a plurality of elongated fingers, each pair of which have converging guide surfaces to guide the routing tool pilot, and hence the cutting tool, in an angular direction as the tool passes through the board to form an axial taper to the slot. The opposite, orthogonal taper, is achieved by the use of a tapered cutting tool, more specifically one that has a wider distal end than at its shank end. That is, the flute diameter at the distal end of the tool has a larger diameter than the flutes where they join the tool shank.
The construction of such dovetailing jigs, and the manner of utilizing such jigs in the cutting of the slots, are described in detail in a Guide entitled "Leigh Dovetail Jig", D4 User Guide, published by Leigh Industries, Ltd., Port Coquitlam, B.C. Canada, copyrighted 1997.
A further problem in the dovetailing systems is that the cuts made must be made, of course, in the board ends prior to assembly, so that they cannot be used to dovetail a joint that has already been assembled, such as an existing furniture piece that needs repair.
There have been also provided in the past miter joint machines for cutting slots at the board ends that receive "biscuits", and sometimes these systems are referred to as "biscuit cutting systems". This system, however, is similar to dovetailing, and not nearly as strong, and includes a guide for cutting a straight internal slot in the mitered end surface of each board prior to assembly. The biscuits are elongated, rectangular pieces that are glued in one slot and then inserted into the slot in the other board as the joint is being assembled.
As noted above, this biscuit miter jointing is not strong and has the disadvantage that it cannot be utilized to provide decorative inserts at the joints because the biscuits are completely internal to the joint itself.
It is a primary object of the present invention to ameliorate the problems noted above in two board corner joints.